The present invention concerns a spinning preparatory machine, in particular a card, with a feeder roll including a body supporting the feeder trough coordinated thereto, a loosening roll provided with points or tips, and with a loosening zone for the fibre material, located between the feeder roll and the loosening roll, and with a suction device located in the converging space formed between the incoming or inbound surface of the loosening roll and the surface of the feeder roll.
In staple fibre yarn spinning the open-end spinning method has found increasing acceptance since this method is more economical in certain yarn count ranges in comparison to the older ring spinning method. In processing natural fibres especially, the open-end spinning method, however, shows the disadvantage, that it reacts susceptibly to the trash present in the fibre slivers to be fed. Mainly the contaminations consisting of micro dust and short fibres are accumulated during the spinning process on the inside rotor wall to which they adhere, which results in the formation of an increasingly uneven yarn and finally results in yarn breakages.
There is no lack of attempts to effectively eliminate contamination of the fibre material in opening and cleaning and in carding. These measures, however, are not sufficient to reach the low content of contaminations, required for open-end spinning, in the fibre material.
In a known card (GB-PS No. 791,339) an air supply opening merges, seen in the direction of rotation of the loosening roll (licker-in or taker-in roll), after the trough nose around which the fibre layer is supplied, through which air supply opening air is sucked into the interior of the perforated loosening roll. The air flowing in the direction towards the loosening roll causes the fibre material already taken over by the licker-in or taker-in roll and stored on its clothing to be pressed into the clothing and to be condensed there, in such manner that the contamination is retained therein.
Also known already in this art is a suction device on cards (DE-AS No. 1,685,552), in which immediately above the feeder roll a suction hood with a suction slot facing the licker-in roll is arranged. The hood is provided for sucking off the fibres clinging to the fluted or knurled feeder roll, the feeder roll being subject to an air flow from both sides, flowing into the hood. Furthermore, only the fibres released by the sharp deflection of the fibre layer supplied at the end of the feeder table trough are to be sucked off using the suction slot, which is desirable in view of their reusability or reworkability. On the other hand, however, a suction device of this type does not permit elimination of contaminations and dust freed from the fibre material during passage over the loosening roll, as the fibre layer, deflected sharply at the end of the trough in the direction of rotation, here widens up or enlarges and forms a throttle. This reduces the effectiveness of the suction stream up to the loosening zone too much, as the latter is located considerably below the deflection point.